I see writing blogs as a way of personal knowledge management. We can have many other ways to manage personal knowledge, using Google Docs, for example.
And then i think, there are countless blogs out there, on the internet. And they are like a huge knowledge mine. At least, they provide huge amount of raw data, and information. That means blog mining can help us acquire valuable knowledge!
So i google 'blog mining'. Surprisingly, it is not very popular, unlike data mining and text mining, although they are related.
No matter what, i still believe blog mining has much potentials. I found two(only two) articles about this topic: